Agitating and mixing compounds in a container is generally done with mixers having impellers producing a flow pattern within the container to achieve the desired results. These impellers are usually of the type straight-blade turbine radial flow, pitched-blade turbine mixed flow or hydrofoil impeller axial flow, depending of the flow pattern required. Dirty accumulations surrounding the work area are usually produced during the mixing process. Therefore, cleaning these mixers often require large quantity of solvents.
Moreover, although these known mixers are appropriate for mixing a large range of compounds, they are not suitable for some others because the impellers may create a lot of friction on the compounds, which can result in substance damage and change.
In addition, good mixing often requires that the impellers mix the content of the entire container, which can be a difficult task to accomplish. Mixing of compounds with these mixers can thus result in poor or uneven mixing of the compounds, poorly dispersed solid particles or their agglomeration.
Known in the art are Japanese Patents Nos 2003/093862 (HIROSHIGE), 2001/276592 (HIROSHIGE) and 2000/271465 (HIROSHIGE), which disclose apparatuses that fully agitate and mix compounds to be kneaded. The apparatuses disclosed in these patents use rotation and revolution to agitate and mix the compounds. These apparatus, also referred to as bladeless mixers, mix the compounds by simultaneously rotating a batch container and revolving it in a planetary motion, thus producing acceleration forces of 400 G and higher. The mixing principle underneath these apparatuses is generated by both centrifugal and centripetal forces. The advantage of such mixers is that they mixed liquids and powders evenly in seconds while imparting no heat. Since the containers are rotated at a predetermined angle, air may be entrapped within the containers. Therefore, once the mixing is complete, an additional step may be required to remove submicron bubbles present within the compounds. Another problem with these apparatuses is that they are very costly and complicated to build, due to their complex mechanical structure.
U.S. Pat. No. 6,334,583 (Li) discloses a planetary-like high-energy ball mill for milling powders. Two cup-like rollers are mounted onto a turntable that is driven in rotation by a vertical main shaft. A mill pot containing the powders to be mixed is fixed within each of the cup-like rollers. A stationary circular ring is mounted over the turntable and is disposed coaxially with the shaft. The cup-like rollers may rotate about their own pivotal shafts while rotating along with the turntable. Sides of the cup-like rollers are in contact with an inner surface of the stationary ring and are therefore rotating about their own pivotal axis due to friction counterforce with the stationary ring. A vertical movement may also be applied to the vertical shaft in order to further mill the powders. One potential problem with such a mill is that at a high velocity of rotation, control over the speed of rotation of the cup-like rollers may be lost if the cup-like rollers spin on themselves. As a result, the uniformity and quality of the milled powder may not be constant. Furthermore, in some cases, the frictional force required to drive into rotation the cup-like rollers upon beginning of rotation of the turntable may not be sufficient. Therefore, there may be a delay before the cup-like rollers may begin to rotate about their own pivotal axis.